Reactivating the mission works like this:
1. You pay a credit for every 10 mission points the mission is worth, rounded up.
2. You complete the mission as normal.
3. You earn the mission points + 10 clintz per mission point. You do NOT earn the Ld or any of the missions' original rewards.

Like before, a LD character is temporarly become availibe, provided you complete the associated missions. If you already have the Legendary Charecter, then compleating the LD missions will give you 10 credits. You can pay to extend the mission's due date (but since I never had to do it, I cannot help you there).